INS and type 2 diabetes mellitus: While insulin resistance is thought to be a primary factor in the pathogenesis of T2D in Caucasian, Mexican–American, and Pima Indian populations (Haffner et al. 1996; Haffner et al. 1988), impaired insulin secretion has been reported to be a major factor in T2D in Japanese (Fukushima et al. 2004a, 2004b; Mitsui et al. 2006).